A data center, where many servers are housed in one location, has become popular in recent years. Because a data center is supposed to house servers in huge quantities with high density, there is a trend toward integrating the redundancy of individual servers from the viewpoint of the relationship between the cost and size.
For example, with the aim of reducing suspension of the service of server devices caused by a power interruption, an uninterruptible power supply (UPS) is used as the server power supply. In this case, typically, a small-capacity UPS is placed on an individual server basis or a rack basis. Alternatively, a plurality of large-capacity UPSs may be placed in a facility, such as a data center, in some cases.
When large-scale UPS devices are used, because one UPS supports an increased number of servers, preferable reliability of the UPS is inevitably higher, as compared with when small-capacity UPSs are used.
One approach to maintaining the reliability of a UPS and ensuring the reliability of a server power supply system is the use of a device called a static transfer switch (hereinafter referred to as “STS”). An STS has two alternating-current power supply input systems as the power supply input; if the power supply input in one system fails, the power input is promptly switched to the other system to continue supplying power to the servers.
FIG. 24 illustrates one example of a server system that uses STSs 241 to 244. In the example illustrated in FIG. 24, servers 280, 284, 285, and 286 include power supply units (PSUs) 245, 246, 247, and 248, respectively. The PSUs 245 to 248 are connected to the respective STSs 241 to 244. In the example illustrated in FIG. 24, because a total of four servers are disposed, the four STSs 241 to 244 in total are disposed.
Each of the STSs 241 to 244 is connected to individually independent power supply systems, that is, an A-side power supply system and a B-side power supply system. In the example illustrated in FIG. 24, the A side is the main power supply system, and the B side is an auxiliary power supply system. If the main power supply system goes down, the STSs 241 to 244 switch the power supply system to an auxiliary system, that is, B-side system to avoid the effects on the server.
FIG. 25 illustrates a schematic configuration of an STS. An STS 250 includes relay switches 253 and 254 disposed therein. The relay switches 253 and 254 include internal coils 252 and 255, respectively. Each of the relay switches 253 and 254 is activated by a controller 251 controlling the coils 252 and 255 and switches the power supply system supplying power the server to one of the A side and B side power supply systems. For example, if the A-side power supply system goes down in the state where the power is supplied from the A-side power supply system, the controller 251 detects this down and controls the relay switches 253 and 254. The control by the controller 251 causes the relay switches 253 and 254 to be switched from the A side to B side, and the power is supplied from the B-side power supply system to a server 256.
UPSs in a data center are typically placed in one specific location of a building. In this case, the wiring between the PSU/STS and the server is long, and that is disadvantages in the cost or easiness of maintenance.
Examples of Patent Literature that discloses a technique relating to a power supply device are listed below.
Japanese Laid-open Patent Publication No. 2001-264367, Japanese Laid-open Patent Publication No. 2002-034177, and Japanese Laid-open Patent Publication No. 2007-215344 are examples of related art.
To protect a server from the effects of an instantaneous power interruption, the power is preferably switched at or below the half cycle of an alternating current. When the frequency of AC power is 60 Hz, the half cycle corresponds to 8 ms; when that is 50 Hz, the half cycle corresponds to 10 ms.
When a semiconductor relay, which generally can operate at high speed, is used in an STS, the PSU can be switched in a period of approximately 1 ms from detection of an instantaneous interruption. In this case, however, there is a problem in that the device is relatively expensive. If the semiconductor relay breaks down, the apparatus moves to a short circuit mode, and thus the STS preferably includes a protective circuit.
In contrast, a mechanical relay is relatively inexpensive, but the length of time of switching is typically at least approximately 5 ms, and this switching time is too long for achieving the switching at or below the half cycle.